You could also add stuff like:
Slipping: A % chance of slipping when making a cut. The harder the cut and the faster the speed, the more likely to slip. Effect could be stronger in snow than rain.
Changes on Pancakes: Increase the chance of both linemen slipping and going down.
Getting up: May take longer to get up and accelerate on a rainy or snowy day.
Temp: On really hot days players loose energy faster.
On really cold days speed would be reduced.
On really cold days players start to warm up the longer they are on the field and cool down the longer they are on the sideline, affecting speed, agi, catching, tackling/break tackles, blocking, str etc.
Moral could be affected for teams playing in the cold when their home region is warm.